Background

Definition

 

Loss of normal ligamentous and / or bony constraints of wrist

 

Anatomy

 

Overall alignment maintained by extrinsic and intrinsic  ligaments

 

1.  Intrinsic ligaments

 

Carpal bone to carpal bone

- support the lunate in a balanced position

 

A.  Scapho-lunate ligaments

 

SL ligament can be divided into three different zones

- dorsal ligamentous zone (structurally the most important)

- palmar ligamentous zone 

- proximal membranous fibrocartilaginous zone

 

B.  Luno-triquetral ligaments 

- also 3 components

- volar most strong

 

2.  Extrinsic Ligaments

 

Radius to carpus 

- obliquely oriented

- resist the tendency of the carpus to migrate ulnarly and palmarly

 

A.  Palmar extrinsic ligaments

 

A. Radioscaphocapitate ligament

B. Radiolunate ligament

C. Radioscapholunate ligament

- probably just a vascular fold

D. Ulnocarpal ligaments

E. Lunotriquetral ligament

 

Space of Poirier

- weak area of the palmar ligaments

 

B.  Dorsal Extrinsics

 

A. Dorsal radiotriquetral ligament / Dorsal radiocarpal ligament (DRC)

B. Dorsal radioulnar ligament

C. Triquetroscaphoid ligament / Dorsal intercarpal ligament (DIC)

 

No tendons attach to proximal row

 

Note: 

- acess to dorsal carpus

- raise a radially based flap

- between radiotriquetral and triquetroscaphoid

- between DRC and DIC

 

Biomechanics

 

Motion

 

Capitate is centre of rotation

 

Flexion / Extension

- 120o

- 50% midcarpal

- 50% radiocarpal

 

Radial / ulna deviation

- 60% midcarpal

- 40% radiocarpal

 

Radial deviation

- 20o

- proximal row and scaphoid flexes

 

Ulnar deviation

- 30o

- proximal row and scaphoid extends

 

Load transfer

 

Radius 80%

Ulna 20% (all via TFCC)

 

Pathology

 

Division of the scapholunate ligament 

- allows the lunate to follow the triquetrum's unrestrained position of extension

- dorsal intercalated segmental instability pattern (DISI)

- scaphoid flexes, lunate extends

 

Lunotriquetral ligament disruption 

- allows the lunate to follow the scaphoid into its position of unrestrained flexion

- lunate flexes

- volar intercalated segmental instability pattern (VlSI)

 

Classification of Carpal Instabilities (Amadio)

 

I. Carpal instability dissociative (CID)

 

Transverse injury

 

Injury inter-osseous ligaments

- within the carpal rows

- disassociative rather than associative motion between the bones of each row

 

A.Dorsiflexion (DISI)

- scapholunate ligament injury

 

B. Palmar flexion (VISI)

- triquetrolunate injury

 

II. Carpal instability non-dissociative (CIND)

 

Transverse injury

 

Normal associative motion between the bones of each carpal row 

- the dissociation is between rows

 

A. Radiocarpal Dislocation

 

CIND Dislocated Radiocarpal Joint APDislocated Radiocarpal Joint lateral

 

Radiocarpal Dislocation CT 1Radiocarpal Dislocation CT 2Radiocarpal Dislocation CT 3

 

B. Midcarpal

 

C. Ulnar Translocation

 

CIND DISI

 

Secondary to radial malunion

- treat with radial osteotomy if symptomatic

 

DISI CIND Secondary Radial Fracture

 

CIND VISI

 

Secondary to ligamentous laxity

- non operative treatment

- no progression to OA

 

Whole proximal row is flexed

- lunate triangular

- scaphoid cortical ring sign

- no SL disassociation

 

III. Carpal instability complex (CIC)

 

Hyperextension injury

 

As the hand is forced into hyperextension

- ulnar deviation and intercarpal supination

- the ligamentous disruption

 

Mayfield Cadaver study 

- extend, ulna deviate, supinate

 

Stage 1 

- SL dissociation 

 

Stage 2

- CL dissociation 

- capitate dislocates

 

Stage 3

-  LT dissociation

 

Stage 4

-  Lunate dislocates

 

Types

 

A. Perilunate Dislocation

1. Dorsal (10%)

2. Volar (90%)

 

B. Trans-scaphoid Perilunate

 

IV. Carpal instability longitudinal (axial)

 

Longitudinal injury

 

The carpus may also be disrupted in a longitudinal fashion, as opposed to the perilunate transverse pattern

 

Classification

 

A.  Axial Ulnar (AU)

B.  Axial Radial (AR)

C. Axial Ulnar-Radial (AUR) / Combined

 

These are severe injuries

- crush, blast or compression

- may be open injuries

- not a diagnostic dilemma

 

Usually wrist is split into two columns

- metacarpals follow their corresponding carpus

 

Management

 

Deal with wounds and nerve / tendon injuries

CTD

K wire fixation

 

Greater and Lesser Arc Injuries

 

Greater arc injury

- fracture-dislocation of the scaphoid, capitate, hamate, triquetrum

- may include radial styloid

 

Lesser arc injury 

- a pure ligamentous injury

- around the lunate